Project Summary/Abstract. The overall focus of my work as a Senior VA Research Career Scientist has been to study the effect of oxidative stress and mitochondrial dysfunction in age-related conditions such as sarcopenia and frailty, and in the neurodegenerative disease, Amyotrophic Lateral Sclerosis (ALS). My research program is highly relevant to the mission of the VA due to the universal impact of sarcopenia and frailty on older veterans, and the increased prevalence of ALS in veterans. Sarcopenia is the progressive loss of muscle mass and function with age characterized by a deterioration of muscle quantity and quality leading to a gradual loss of activity and a decline in strength and power. Sarcopenia has a critical impact on the aging population and older Veterans (more than 40% of veterans are over age 65) due to the increased risk of falls and injuries, leading to excess morbidity and mortality. An understanding of the factors and interactions in the mechanisms involved in motorneuron health, maintenance and eventual degeneration of the neuromuscular junction (NMJ), synaptic function and degenerative changes in the muscle tissue itself are critical to identify potential therapeutic targets to prevent or reduce muscle atrophy during aging and in neuromuscular degenerative diseases such as ALS. In my most recent completed VA merit review project ?Testing the mechanisms by which NMJ disruption contributes to sarcopenia? we specifically investigated the role of the neuromuscular junction and loss of innervation in muscle atrophy and weakness. Using several novel mouse models to target deficits in neurons alone, muscle alone or in both tissues, we tested whether alterations in the neuromuscular junction play a critical role in sarcopenia by modulating the NMJ through presynaptic and postsynaptic alterations and measuring the effect on downstream degenerative pathways in muscle. Key findings from these studies show that changes in the neuron are important, and likely initiate changes in the muscle, yet deficits in both the neuron and the muscle are required to initiate a full sarcopenic phenotype. Importantly, we further demonstrated that rescuing neuronal deficits specifically in neurons in a CuZnSOD (Sod1-/-) knockout mouse that mimics accelerated age related sarcopenia is sufficient to preserve neuromuscular junction and skeletal muscle structure despite the high levels of overall oxidative stress in this model. These results suggest that redox homeostasis in motor neurons plays a key role in initiating sarcopenia during aging and that therapies to reduce muscle atrophy during aging may be most effective if they target the motor neurons. Another key result from the studies in the past funding period formed the basis for our new studies that point to maintenance of cytosolic calcium as a potential regulator of downstream muscle degenerative changes. We found that the loss of muscle mass and function in the Sod1-/- mouse model could be prevented using an activator of the SERCA ATPase pump that returns calcium form the cytosol to the sarcoplasmic reticulum following contraction. We hypothesized that interventions to activate the SERCA ATPase and improve calcium homeostasis in skeletal muscle or motor neurons can reduce muscle atrophy and weakness in aging. This is the focus of my recently funded VA Merit grant and we are optimistic these studies will establish potential new interventions to preserve muscle mass and function in aging veterans. In summary, the long term goals for my research program are to determine the underlying mechanisms of muscle fiber loss and muscle weakness with aging and to define the relative contributions of the motor neuron and muscle in NMJ deterioration and age-related muscle atrophy and diseases associated with neuromuscular degeneration. I aim to identify potential interventions to improve muscle quality and strength in older veterans and contribute in a positive way to increased healthspan and quality of life.